The present invention relates generally to thermal radiators and more particularly has reference to thermal radiators with a thermal emissivity function which is strongly wavelength dependent.
Known refractory materials have a thermal emissivity function which is strongly wavelength dependent. For example, the materials may have high emissivity (and absorption) at the infrared wavelengths, high emissivity in the visible wavelength range, and very low emissivity at intermediate wavelengths. If a material having those emissivity characteristics and a black body are exposed to IR beams of equal intensity, the selective thermal radiator will emit visible radiation with higher efficiency (if radiation cooling predominates), i.e., the selective thermal radiator will appear brighter than the black body. This effect is known as the Welsbach effect and is extensively used in commercial gas lantern mantles.
Infrared (IR) monitoring and control is now done primarily by radiometers and thermocouples, which are of low resolution and inconvenient, or semiconductor devices. There is a need for a device which permits simple visual observation of the intensity of IR energy.